Instantaneous recording composition



Patented Sept. 3, 1946 INSTAN TAN EOUSFREGORDING COMPOSITION rAlbert "B. Savage, 'Midland Micn, eassign-or toiThe -Dow Chemical -.Company, .-Midland, .Mich., ..a

. corporation 011 Michigan No Drawing. -Application Decenibei 3L I942,

Serial No. 470,912

This: invent-ion :relates tow-a :"sound record iaand particularly to: za-record "Offit'hfi. instantaneous: recording type characterized by its low surface noise and high fidelity after many playings.

l'IThe: methods f forming soun'd tracks E in rec ords are well knownLinat-he art. The method whereby the sound track is for-meddirectly in therecordrsurface in response to the sound actuated 'pick-up device is usually designated as In- "stantaneous' Recording as contrasted with other methodswhereby the track is impressed in the *record'surface' by means 6f a previously'formed -'die or matrix. -Record blanks for-instantaneous .-recor'ding .may' be in the form of..discs,:;cylinders,

*fiexible tape, 1100135, -etc. The isourid :track "in suchinstantaneous recording records is usually formed by slitting, cutting or otherwise operating on the surface of the record blank with a sound actuatedrecordingstylustoleave a sinu- *ousgroove'which" the :playing stylus will follow to repro duce the recorded sound.

The composition from which the record blank .isunade has considerable influence not only upon the"'f1dellty "of "the "reproduction .but also upon the amountof extraneousmoise heard when the record is played. :'Thus,;if the composition 'istoo hard 'therecordingrstylus"will .not cut smoothly through it"during' the" recording and the surface of the soundtrack-"instead of being. smooth, will be'roughdue' totearing orchipping by the stylus. Such rough 'sur'face'd sound tracks lead to high noise'ievels "duringtheplaying of the record. Records made from excessively hard material are alsosubjectto deterioration due to the breaking Ofbduringuse and handlin of the minute projections. in thesound track which serve to actuate theplayirrgstirlus. Such deterioration. soon leads tolackfof fidelity inithe reproduction. On'the otherhairdrecords' made fron too. soft .a composition are subject to excessive Wear" by the, playing..sty1us ...and-consequent loss of fidelity after a few playings. Other properties of the composition from which the record blank is made are also of importance. Thus, if the material is too elastic the cutting stylus will tend to slide over the surface rather than out cleanly through it. When compositions are used which are subject to embrittlement upon aging, it is apparent that the value of the record will depreciate.

Record blanks for instantaneous recording have heretofore usually been made from nitro cellulose compositions because these have been found to possess the desired degree of hardness and elasticity. Such compositions are, however, subject to the serious objection that nitro cellulose is highly inflammable and presents -aconsiderableifire hazard. %Nitro cellulose compositionsrare furthermore subject to considerable cembrittlemerit-upon aging. -Attempts to usenethyls'cellu- =lose-compesitions have also been. made,- bnt .rec- Jordsqarepared: from the hGI-GtOfOIG'HSEd compe- -sitions-eareri-nvariably :noisy and 01 rinferiorgualf It there-fore, "an: object of the inventiontto provide a .:composition adapted lto-the manufacture of instantaneous 'recording \sound .IBCOIdS -having.--a highifi-delity of reproduction and: alow noise val-ue -iafter repeated playing.

An additional object is to provide a-sound-rrec- 0rd blank having azlow firerhazard and adapted .to having formed thereon a high fidelity sound trackiby instantaneous recordin methods.

' These and related objects ar readily'accom- .plishedzby plasticizing ethyl cellulose with ailower 'a'lkylesterof ricinoleic"acid. Record'blanks'preparedirom such compositions are'easilyfcutor embossed by'ithe recording stylus duringinstan- .taneousrecor'ding' to" produce soundtracks free from'extraneous irregularities and" surface roughness, Thefinished records are'particularly'char- .acterized by their. low degree of .infiammability. iDueitU'thetOughneSS of the composition'and its lack of embrittlement upon aging, there is little tendency "for the playing. stylus to wear away the soundtrack such as isv the'cas whenot'her plasticizersfor the ethyl'cellulose are used. Consequently,'the records. may be playe'd'back' many .times without diminishing the quality dfthe recording or; raising undulythe noise level of the record.

Drgano-soluble ethyl cellulose having. an ethoxy content of, from 45.5 'to 49.5.percent, .and preferably of from 48' to 49 percent, and anintrinsicviscosity of from 5 to 100,.centipoises, when determined in ..the Ubbelohdeviscosimeten on a 5 per .cent by weight. solution in, a. mixture -of parts by volume of toluene and 20 parts of ethanol, may be used in preparing the composition. Ethyl cellulose of such ethoxy content and intrinsic viscosity is readily available commercially. From 50 to per cent by weight of ethyl cellulose may be used in the composition. Lower alkyl esters of ricinoleic acid which may be used as plasticizers in preparing the composition include the methyl, ethyl, propyl, butyl, n-octyl, 2-ethyl-hexyl, decyl, and lauryl esters. Alkyl esters having from 1 to 12 carbon atoms inclusive in the alkyl group may be used to particular advantage. The lower alkyl esters of an acyl ricinoleic acid, e. g. of acetyl ricinoleic acid,

.is desired, less plasticizer may be used than when a relatively soft blank is desired. In certain instances minor amounts of relatively non-volatile plasticizers other than the alkyl ricinoleates, such as the aryl phosphates, the alkyl phosphates, the soft, non-oxidizing resinous plasticizers, etc., may also be incorporated in the composition, if desired. Fillers, pigments, soluble dyes, and other modifying agents may also be incorporated in the composition.

In practicing the invention the ethyl cellulose composition may be molded in the form of discs, or cylinders, or the ingredients may be dissolved in a volatile solvent and the solution used in the casting of films which may be subsequently cut or trimmed to the desired size. Discs or cylinders composed of other materials may, if desired, be surface-coated with the composition and the sound track may be formed in the coating.

Certain advantages of the invention may be seen from the following example which is merely by way of illustration and is not to be construed as limiting.

EXAMPLE A composition was prepared by dissolving 75 parts by weight of ethyl cellulose, having an ethoxy content of about 48 per cent and a viscosity of about centipoises and 25 parts of methyl ricinoleate in 235 parts of a mixture of 80 parts by volume of toluene and parts of ethanol. The mixture was stirred until solution was complete, centrifuged toremove a small amount of insoluble matter and poured onto a polished aluminum disc about 10 inches in diameter. The disc was spun horizontally until the solution had spread evenly over its surface, and then placed in a dust free cabinet to dry. The record blank was air dried for 16 hours at room temperature and then oven dried at 90 C. for 6 hours and placed in a constant temperature room at C. for testing. The dried film on the aluminum plate was about 0.01 inch thick. Similar record blanks were prepared using 25 parts of ethyl ricinoleate, isopropyl ricinoleate, butyl ricinoleate, and by way of comparison of monophenyldi-(o-xenyl) phosphate, as plasticizers in place of the methyl ricinoleate.

To test the record blanks for extraneous noise accompanying recording, they were each placed on a recording machine and rotated at 78 revolutions per minute. An unmodulated groove was cut at the same radius in each blank with the same recording stylus with no input to the recording head. The records were then played back and the volume of noise was determined with a cathode ray oscillograph. The deflection of the oscillograph was measured in millimeters and the measured values converted to decibels by the formula:

Decibels=20 log where E2 is the measured reading of the oscillograph and E1 is an arbitrary constant value chosen equal to the lowest reading observed in any of the tests.

Each record was played a number of times. The noise level of each after 1, l0 and 20 playings is recorded in the accompanying table. The low noise level after repeated playing characteristic of records made from the composition containing the ricinoleate plasticizers is apparent.

I claim:

1. A sound record of the instantaneous recording type, the composition whereof includes ethyl cellulose and as a plasticizer therefor a lower alkyl ester of ricinoleic acid.

2. A sound record as claimed in claim 1 wherein the ethyl cellulose has an ethoxy content of from 45.5 to 49.5 per cent and an intrinsic vis cosity of from 5 to 100 centipoises.

3. A sound record as claimed in claim 1 wherein the amount of ethyl cellulose is from 50 to per cent by weight of the composition.

4. A sound record as claimed in claim 1 wherein the amount of the alkyl ricinoleate plasticizer is from 5 to 40 per cent by weight of the composition.

5. A sound record as claimed in claim 1 wherein the alkyl ricinoleate plasticizer has from 1 to 12 carbon atoms in the alkyl group.

6. A sound record as claimed in claim 1 wherein the ricinoleate plasticizer is butyl ricinoleate.

7. A sound record as claimed in claim 1 wherein the ricinoleate plasticizer is 2-ethyl-hexyl ricinoleate.

ALBERT B. SAVAGE. 

